The present invention relates to antistatic acrylic polymers, and more specifically to a composition comprising an acrylic polymer (A), a copolymer (B) containing polyamide blocks and polyether blocks essentially comprising ethylene oxide xe2x80x94(C2H4xe2x80x94O)xe2x80x94 units, and a polymer (C) chosen from acrylic impact modifiers and/or functional polymers.
It is concerned with giving the acrylic polymer (A) antistatic properties. The formation and retention of static electricity charges at the surface of most plastics are known. The presence of static electricity on thermoplastic films leads, for example, to these films sticking together, making them difficult to separate. The presence of static electricity on wrapping films can cause the accumulation of dust on the objects to be wrapped and thus inhibit their use. Acrylic resins such as, for example, PMMA are used to make different objects, and in particular transparent objects. Static electricity causes the accumulation of dust at the surface of these objects, which is an inconvenience as regards the transparency.
The prior art discloses antistatic agents such as ionic surfactants of the sulphonate or ethoxylated amine type which are added to polymers. However, the antistatic properties of the polymers depend on the ambient humidity and they are not permanent since these agents migrate to the surface of the polymers and disappear. Polymers containing polyamide blocks and hydrophilic polyether blocks have thus been proposed as antistatic agents, these agents having the advantage of not migrating and thus of giving permanent antistatic properties that are more independent of the ambient humidity.
The aim of the present invention is to give a permanently antistatic nature to commercially available acrylic resins, i.e. (i) resins consisting essentially only of acrylic polymer or (ii) resins consisting of a mixture of acrylic polymer and of an impact modifier. Another aim of the invention is also to improve the impact behaviour, in particular the multiaxial impact behaviour. As regards transparent PMMA, the aim is also not to adversely affect the transparency.
Japanese patent application JP 60 023 435 A published on Feb. 6, 1985 discloses antistatic combinations comprising 5 to 80% of polyether-esteramide and 95 to 20% of a thermoplastic resin chosen, inter alia, from polystyrene, ABS and PMMA, this resin being functionalized with acrylic acid or maleic anhydride. Examples show compositions consisting of 60 to 70 parts of carboxylated PMMA and 40 to 30 parts of polyetheresteramide (per 100 parts). Others show compositions consisting of 30 to 45 parts of carboxylated PMMA, 40 to 25 parts of PMMA and 30 parts of polyetheresteramide (per 100 parts). Nothing is written regarding the transparency of PMMA-based compositions and, what is more, it is necessary to have available carboxylated PMMA in large proportions.
Japanese patent application JP 03 237 149 A published on Oct. 23, 1991 discloses antistatic compositions consisting of 40 to 99% of an acrylic resin, 1 to 60% of polyetheresteramide and 0.2 to 15% of a grafted polymer containing maleic anhydride or epoxide functions and a portion which is soluble in the acrylic resin. The grafted polymer is complicated to prepare.
Japanese patent applications JP 08 253640 A published on Oct. 1, 1996 and JP 04 146 947 A published on May 20, 1992, disclose antistatic and transparent compositions consisting of acrylic resin, polyetheresteramide and salts. It is not desirable to add salts to such compositions since they may later migrate when the compositions are used.
Japanese patent applications JP 05 295 213 A published on Nov. 9, 1993 and JP 05 287 157 A published on Nov. 2, 1993 disclose antistatic and transparent compositions consisting of acrylic resin, polyetheresteramide and optionally an electrolyte or sulphonic acid. They have the same drawback as the above compositions.
Japanese patent applications JP 05 078 543 A and JP 04 146 947 A disclose antistatic and transparent compositions consisting of acrylic resin and polyetheresteramide. The mechanical properties of the base resin are greatly impaired.
Novel antistatic acrylic resin compositions have now been found. To give a permanently antistatic nature to commercially available acrylic resins, i.e. (i) resins consisting essentially only of acrylic polymer or (ii) resins consisting of a mixture of acrylic polymer and of an impact modifier, it suffices to add thereto a polyetheresteramide and optionally certain functional polymers. Another advantage of the invention is also to improve the impact properties, in particular the multiaxial impact properties. As regards transparent PMMA, the advantage is also not to adversely affect the transparency.
The present invention thus relates to an antistatic composition having improved impact strength behaviour, comprising, per 100 parts by weight:
95 to 80 parts of (A)+(C),
5 to 20 parts of (B),
(A) being an acrylic polymer,
(B) being a copolymer containing polyamide blocks and polyether blocks essentially comprising ethylene oxide xe2x80x94(C2H4xe2x80x94O)xe2x80x94 units,
(C) being a polymer chosen from acrylic impact modifiers, low-mass copolymers (C1) of styrene and of an unsaturated carboxylic anhydride, copolymers (C2) of ethylene and of an unsaturated carboxylic anhydride, copolymers (C3) of ethylene and of an unsaturated epoxide, or mixtures thereof.
The Applicant has discovered that the invention is particularly useful for impact-modified PMMA, i.e. a mixture of (A) and of an acrylic impact modifier (C). To give this composition an antistatic nature without it being necessary to add one or more of the copolymers (C1) to (C3), it suffices to add (B) thereto. Furthermore, the transparency is not substantially adversely affected. Another advantage is that the mixture of the impact-modified PMMA and of (B) can be prepared by dry blending and introduced directly into the injection or moulding device without it being necessary to prepare an intimate mixture in an extruder or blender.
Examples of acrylic polymers (A) which may be mentioned are alkyl (meth)acrylate homopolymers. Alkyl (meth)acrylates are described in Kirk-Othmer, Encyclopedia of chemical technology, 4th edition, in Vol. 1, pages 292-293 and in Vol. 16, pages 475-478. Mention may also be made of copolymers of at least two of these (meth)acrylates and copolymers of at least one (meth)acrylate with at least one monomer chosen from acrylonitrile, butadiene, styrene and isoprene, provided that the proportion of (meth)acrylate is at least 50 mol %. The invention is particularly useful for PMMA. These acrylic polymers either consist of monomers and optionally of the comonomers mentioned above and contain no impact modifier, or they additionally contain an acrylic impact modifier. The acrylic impact modifiers are, for example, random or block copolymers of at least one monomer chosen from styrene, butadiene and isoprene and of at least one monomer chosen from acrylonitrile and alkyl (meth)acrylates, and they may be of core-shell type. These acrylic impact modifiers can be mixed with the acrylic polymer (A) once prepared or can be introduced during the polymerization of (A) or prepared simultaneously during the polymerization of (A). The melt flow index of (A) may be between 2 g/10 min and 15 g/10 min measured at 230xc2x0 C. under a load of 3.8 kg.
The amount of acrylic impact modifier may be, for example, from 0 to 30 parts per 100 to 70 parts of (A) and advantageously from 5 to 20 parts per 95 to 20 parts of (A).
It would not constitute a departure from the invention if (A) was a mixture of two or more of the above polymers.
The polymers (B) containing polyamide blocks and polyether blocks result from the copolycondensation of polyamide sequences containing reactive ends with polyether sequences containing reactive ends, such as, inter alia:
1) polyamide sequences containing diamine chain ends with polyoxyalkylene sequences containing dicarboxylic chain ends,
2) polyamide sequences containing dicarboxylic chain ends with polyoxyalkylene sequences containing diamine chain ends, obtained by cyanoethylation and hydrogenation of aliphatic xcex1,xcfx89-dihydroxylated polyoxyalkylene sequences, known as polyetherdiols, 3) polyamide sequences containing dicarboxylic chain ends with polyetherdiols, the products obtained being, in this specific case, polyetheresteramides. The copolymers (B) are advantageously of this type.
The polyamide sequences with dicarboxylic chain ends are obtained, for example, from the condensation of xcex1,xcfx89-aminocarboxylic acids, lactams or dicarboxylic acids and diamines in the presence of a chain-limiting dicarboxylic acid.
The number-average molar mass {overscore (M)}n of the polyamide sequences is between 300 and 15000 and preferably between 600 and 5000. The mass of the polyether sequences is between 100 and 6000 and preferably between 200 and 3000.
The polymers containing polyamide blocks and polyether blocks can also comprise randomly-distributed units. These polymers can be prepared by simultaneously reacting the polyether and precursors of the polyamide blocks.
For example, polyetherdiol, a lactam (or an xcex1,xcfx89-amino acid) and a chain-limiting diacid can be reacted in the presence of a small amount of water. A polymer essentially containing polyether blocks, polyamide blocks of very variable length, and also the various reagents which have reacted randomly and which are distributed randomly along the polymer chain, is obtained.
These polymers containing polyamide blocks and polyether blocks, whether they are obtained from the copolycondensation of polyamide and polyether sequences prepared beforehand or from a one-step reaction, have, for example, shore D hardnesses which may be between 20 and 75 and advantageously between 30 and 70, and an intrinsic viscosity of between 0.8 and 2.5, measured in meta-cresol at 250xc2x0 C. for an initial concentration of 0.8 g/100 ml. The MFI values may be between 5 and 50 (235xc2x0 C. under a 1 kg load).
The polyetherdiol blocks are either used as they are and copolycondensed with polyamide blocks containing carboxylic ends, or they are aminated in order to be converted into polyetherdiamines and condensed with polyamide blocks containing carboxylic ends. They can also be mixed with polyamide precursors and a chain limiter in order to prepare polymers containing polyamide blocks and polyether blocks having randomly distributed units.
Polymers containing polyamide and polyether blocks are described in patents U.S. Pat. No. 4,331,786, U.S. Pat. No. 4,115,475, U.S. Pat. No. 4,195,015, U.S. Pat. No. 4,839,441, U.S. Pat. No. 4,864,014, U.S. Pat. No. 4,230,838 and U.S. Pat. No. 4,332,920.
According to a first form of the invention, the polyamide sequences containing dicarboxylic chain ends are obtained, for example, from the condensation of xcex1,xcfx89-aminocarboxylic acids, lactams or dicarboxylic acids and diamines in the presence of a chain-limiting dicarboxylic acid. An example of an xcex1,xcfx89-aminocarboxylic acid which may be mentioned is aminoundecanoic acid, examples of lactams which may be mentioned are caprolactam and lauryllactam, examples of dicarboxylic acids which may be mentioned are adipic acid, decanedioic acid and dodecanedioic acid, and an example of a diamine which may be mentioned is hexamethylenediamine. The polyamide blocks are made of nylon-12 or nylon-6. The melting point of these polyamide sequences, which is also that of the copolymer (B), is generally 10 to 15xc2x0 C. below that of the PA-12 or PA-6.
Depending on the nature of (A), it may be useful to use a copolymer (B) which has a lower melting point so as not to degrade (A) during the incorporation of (B), and this forms the subject of the second and third forms of the invention below.
According to a second form of the invention, the polyamide sequences result from the condensation of one or more xcex1,xcfx89-aminocarboxylic acids and/or of one or more lactams containing from 6 to 12 carbon atoms in the presence of a dicarboxylic acid containing from 4 to 12 carbon atoms and of low molecular mass, i.e. {overscore (M)}n of 400 to 1000. Examples of xcex1,xcfx89-aminocarboxylic acid which may be mentioned are aminoundecanoic acid and aminododecanoic acid. Examples of dicarboxylic acids which may be mentioned are adipic acid, sebacic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulphoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated) and dodecanedioic acid HOOCxe2x80x94(CH2)10xe2x80x94COOH.